A gas leaking through a gap of a piston ring into a crankcase during engine compression and explosion strokes is generally called blow-by gas. The blow-by gas, which fills the crankcase and a cylinder head cover communicating therewith, needs to be released outside.
However, the crankcase has therein a crankshaft, a connecting rod and the like which move fast, and the cylinder head cover communicating with the crankcase has therein a rocker arm, a valve and the like which are in work, so that the crankcase and the cylinder head cover are full of oil mist.
Accordingly, mere release of the blow-by gas to the atmosphere results in discharge of also the oil mist mixed with the blow-by gas to outside, leading to increase in engine oil consumption as well as to environmental pollution. For these reasons, a recent diesel engine is also provided with a closed breather which is operated by a negative pressure of an intake system to return the blow-by gas to the intake system and which is capable of collecting and removing the oil mist contained in the blow-by gas, thereby preventing the blow-by gas from being discharged to the atmosphere.
FIG. 1 shows an example of an intake system in a conventional diesel engine. Reference numeral 1 denotes a diesel engine body; 2, a cylinder head cover of the body 1; 3, an intake manifold connected to the body 1; 4, an intake pipe connected to the manifold 3; 5, an air cleaner connected to the pipe 4; and 6, an airflow meter for measuring a flow rate of air flowing through the pipe 4. A blow-by gas vent tube 7 has one end connected to the cylinder head cover 2 and has the other end connected to a closed breather 8 capable of collecting and removing oil mist contained in the blow-by gas. A blow-by gas return tube 9, which returns to the intake pipe 4 the blow-by gas from which oil mist has been collected and removed by the closed breather 8, has one end connected to the closed breather 8 and has the other end with a return port 10 connected to the pipe 4 downstream of the airflow meter 6.
In FIG. 1, reference numeral 11 denotes an oil mist collection tube connected to a bottom of the closed breather 8 to return to an oil pan (not shown) the oil mist collected and removed from the blow-by gas by the breather 8.
In operation of the diesel engine body 1, clean air filtered by the air cleaner 5 is taken into the diesel engine body 1 through the intake pipe 4 and manifold 3. At this time, the closed breather 8 is operated by the negative pressure of the intake pipe 4 to return the blow-by gas to the pipe 4 while the oil mist contained in the blow-by gas is collected and removed, thereby preventing the blow-by gas from being released to the atmosphere, reducing the oil consumption and preventing environmental pollution. Since the return port 10 for return of the blow-by gas by the closed breather 8 to the intake pipe 4 is connected thereto downstream of the airflow meter 6, there is no fear that the oil mist remaining without thoroughly removed from the blow-by gas adheres to a tip of the meter 6, thereby preventing an accuracy of air-flow-rate measurement by the airflow meter 6 from being lowered and enabling fine control of a fuel/air mixing ratio, leading to exhaust gas purification.
The conventional diesel engine shown in FIG. 1 is disclosed, for example, in Patent Literature 1.